ScriptTask should allow for handling script execution errors

* caught exceptions are turned into WorkflowTaskExecException pointing to failed task
* task state is set to WAITING - we do not want it to stay marked as COMPLETED

SpiffWorkflow/bpmn/specs/ScriptTask.py

@@ -16,9 +16,14 @@
 # License along with this library; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 # 02110-1301  USA
+import logging
 
 from .BpmnSpecMixin import BpmnSpecMixin
+from ...task import Task
 from ...specs.Simple import Simple
+from ...exceptions import WorkflowTaskExecException
+
+LOG = logging.getLogger(__name__)
 
 
 class ScriptTask(Simple, BpmnSpecMixin):
@@ -40,5 +45,13 @@ def _on_complete_hook(self, task):
         if task.workflow._is_busy_with_restore():
             return
         assert not task.workflow.read_only
-        task.workflow.script_engine.execute(task, self.script)
+        try:
+            task.workflow.script_engine.execute(task, self.script)
+        except Exception:
+            LOG.error('Error executing ScriptTask; task=%r', task, exc_info=True)
+            # set state to WAITING (because it is definitely not COMPLETED)
+            # and raise WorkflowException pointing to this task because
+            # maybe upstream someone will be able to handle this situation
+            task._setstate(Task.WAITING, force=True)
+            raise WorkflowTaskExecException(task, 'Error during script execution')
         super(ScriptTask, self)._on_complete_hook(task)